Prior art conveyor ovens are shown in U.S. Pat. Nos. 4,964,392 and 5,277,105 owned by the assignee of this invention and in the references cited on the cover pages of these patents. These and other similar patents may be consulted in order to learn details of how conveyor ovens are constructed and operate. Often—but not always—this type of oven is used to cook or bake pizzas, bread, or the like.
Conveyor ovens are devices for automatically baking or cooking food products over timed periods. Normally, they have a conveyor belt which travels through an elongated oven cavity having open ends and at a speed which times the exposure of the food product to the heat of the oven. A food product, such as a pizza, for example, is placed on one end of the conveyor at the entry to the oven cavity and delivered from the oven at the opposite end of the cavity. The heat in the oven and the speed of the conveyor are coordinated so that the food product is fully and correctly cooked or baked by the time when the conveyor delivers it at the exit end.
The conventional method of delivering controlled heat has been to switch burners off and on in order to hold the resulting temperature in the oven cavity within a relatively narrow range. This process has functioned very well in the past. However, anything can always be improved and, therefore, it is always possible to do a better job heating and cooking or baking the food product.
Also, the cost of the fuel (natural or propane gas) for the burners is increasing sharply. Thus, an important goal is to reduce the fuel consumption, which the invention has done by approximately 30%.
A conveyor oven is usually energized by gas, which always requires a safety feature since an explosive atmosphere might be created by leaking gas. As a result, various governmental agencies prescribe an incorporation of safety features, such as a cut-off valve, into the design of the oven. It is important for the oven controls to be designed to not only enable a reliability of these safety features, but also to provide a redundancy for the safety features. In this invention, the safety features are enhanced by providing an electrical isolation between control signals that might otherwise cause a feed back that might enable the oven to continue operation or to re-ignite after a demand for shut down.